The composition and bioavailability of phosphorus transport through the Changjiang (Yangtze) River during the 1998 flood

Water and suspended sediment (SS) samples were collected from the Changjiang River at the Datong Hydrological Station (DHS), five times from May 1997 through January 1999 in order to evaluate transport, composition and bioavailability of phosphorus (P) during a 1998 flood. Transport of most of the phosphorus compositions was substantially higher during the 1998 flood than at other sampling dates. Phosphorus associated with suspended sediment (TPP) accounted for more than 85% of total phosphorus (TP) transport during periods of preflood and flood. The high transport of TPP during the flood was due to unusually high concentrations of TPP and sediment discharge. The potentially bioavailable phosphorus in SS (PBAP) accounted for about 10% of TPP. PBAP with dissolved inorganic phosphorus (DIP) consisted of 15-89% of TP. For all the sampling dates, the concentrations of potential bioavailable phosphorus (BAP) ranged from 0.035-0.08 mg L-1, significantly higher than the limiting concentration for eutrophication. Therefore, the increasing temporal trends of TP concentration and high bioavailability of TP appear to support more frequent algal blooms in receiving East China Sea coastal waters in recent years. Hence, the underestimate of TPP transport by large rivers may also underestimate the biogeochemical cycling of other associated nutrients, such as nitrogen and carbon.